As every year, the Ministry of Health is implementing, from May 1st to November 30th, a period of Enhanced surveillance of arboviruses in metropolitan France. This campaign aims to increase vigilance against mosquitoes, in particular tiger mosquitoesvectors of the viruses responsible for these diseases.

Indeed, since the beginning of 2026, a significant number of dengue and chikungunya cases have been observed in metropolitan France, with:

This development underlines the importance of the vector control against tiger mosquitoes, particularly during the period of mosquito activity, which is conducive to their proliferation.

The increase in the number of cases indigenousThat is, infected within the national territory without prior travel, is often linked to theabsence of diagnosis, underreporting or late reporting of these casesIt is therefore essential to diagnose cases quickly through appropriate biological tests, to report cases as soon as possible when results are positive, and to be vigilant regarding the presence of mosquitoes in and around premises.

To better understand the issues related to this enhanced surveillance, here are 5 essential things to know about arboviruses:

Arboviruses: definition and causative agents

Arboviruses are diseases caused by arbovirus, a virus transmitted to humans but also to other vertebrate species by certain blood-sucking arthropods (which feed on blood) such as mosquitoes, ticks, sandflies or Culicoides.

La dengue, chikungunya and the Zika are examples of arboviruses transmitted by mosquitoes, and in particular by the tiger mosquitoes gender Aedes. The West Nile virus is also an arbovirus transmitted by the common mosquitoes gender Culex.

Presence of tiger mosquitoes, vectors of arboviruses, in France

The tiger mosquito of the genus Aedes albopictusOriginating in Asia, it has expanded significantly in metropolitan France since 2004. By early 2025, 81 of the 96 French departments were colonized by this mosquito. The departments of South of France are the most heavily colonized.

Symptoms associated with arboviruses

Symptoms vary depending on the virus, but in most cases, infection with dengue, chikungunya, Zika, or West Nile virus is asymptomatic (in 50 to 90% of cases).

When present, symptoms include:

More serious forms can occur with pulmonary, neurological or hemorrhagic disorders which can go up to death.

What pprotection against arboviruses ?

There is currently no specific treatment for arboviral diseases. Management is based primarily on symptomatic treatments.

Prevention relies on individual protective measures: use of repellents, port covering, long and loose-fitting clothing, the use of fans and installation of mosquito netsIt is also essential toeliminate stagnant water, which constitute larval habitats for mosquitoes.

These measures, combined with the epidemiological surveillance and early detection These cases help to strengthen vector control efforts.

The vaccines vaccines against dengue and chikungunya are used for prevention, but their use remains limited to specific populations.

Challenges of enhanced surveillance in France

In a context of increasing cases of dengue and chikungunya in metropolitan France, probably linked to the spread of the tiger mosquito, it is essential to diagnose and report cases as early as possible possible in order to limit the occurrence of new infections, particularly during the period between May and November, the active mosquito season. It is important to remember that the dengue, chikungunya, Zika West Nile fever and other diseases are notifiable year-round.

Climate change, urbanization, and the intensification of international trade are facilitating the gradual establishment of mosquito vectors in Europe. Arboviruses illustrate the challenges of global health ("One Health"), linking human health, the environment, and ecological dynamics.

To learn more about mosquito-borne arboviruses, also consult our disease fact sheets dedicated to dengue, chikungunya and Zika.

Before travelling to a risk area, find travel advice and appropriate health recommendations on the Metis app from the Pasteur Institute of Lille.

Article written by the Dr. Doriane Henry, in charge of scientific communication at thePasteur Institute of Lille (IPL).

FAQ

Arboviruses are viral diseases, such as dengue, chikungunya or Zika, transmitted to humans by mosquitoes or other arthropods.

In metropolitan France, the tiger mosquito of the genus Aedes albopictus is the main vector of arboviruses.

In most cases arboviral diseases are asymptomatic, but flu-like symptoms may appear such as a sudden fever, muscle and/or joint pain, headaches accompanied by a skin rash.

Yes. In some cases, neurological, hemorrhagic or pulmonary complications can occur, which may lead to death.

The tiger mosquito is established in the majority of French departments, particularly in the south and is progressively expanding towards the north.

Arboviruses are transmitted through the bite of an infected mosquito or other arthropod. Human-to-human transmission (mother-to-child transmission, blood transmission, sexual transmission), primarily documented for Zika, is exceptional.

Using repellents, wearing long, loose-fitting clothing that covers the skin, using fans, and installing mosquito nets are all recommended. Eliminating stagnant water is also advised.

There is no specific treatment for arboviruses. Management focuses on treating the symptoms.

To quickly detect cases, limit local transmission and reduce the risk of an epidemic in metropolitan France.

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